Nobody Breathe!!!


 
D

Darren C.

TVWBB Pro
I think I may have finally got my PID dialed in on my Akorn (P=3 I=0.001 D=15)!!!!!!

FWIW, I shut the top vent down onto an 1/8" drill bit to measure the opening. So, if that little tidbit helps anyone.

I have a bad feeling this won't last (or be repeatable, is what I mean). But, I'm crossing my fingers. I got off to a rocky start. And, this has been burning for about 24 hrs. So, there can't be much charcoal left. I didn't start with a whole lot, maybe a chimney of lump or so?? Not exactly sure.

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I have had a lot of issues with my Akron that I've been unable to fully tackle. I'm on vacation so don't have my settings handy, but I've multiple times have had settings which has kept the temperature stable for a few hours, and then it starts wildly fluxuating. I'm guessing it has to do with placement of the lump/airflow that I still havent gotten right. I'm not sure how if this has to do with an Akron vs an actual ceramic (though I'm going to try and use this as an excuse to pickup a big joe next time I see one on sale)
 
Have you considered dialing back the blower power? I'm no PID expert, but looking at your graphs makes me think this may be a quick fix.
 
Bill Herbert said:
Have you considered dialing back the blower power? I'm no PID expert, but looking at your graphs makes me think this may be a quick fix.
Click to expand...

I'm hopeful that my current PID parameters are going to work for me. Note the graph changed after 12:15. That's where I think I got PIDs "dialed in". I'm really holding my breath at this point. I haven't had a chance to do another long test since getting the PID set. I hope to try one at 225 with lump today. But, I did do a short cook at 425 yesterday. I was actually amazed at how well it dialed up to 425 and stayed there.

Thanks for the suggestion.
 
@Bill - I hope I'm not too late. You can breathe now:).

I'm doing another test today. This time, at 225 with a weber chimney of Kingsford. I tried lump last night twice, but the fire went out both times. I'm not too sure if it's me or the lump. I'll figure that out later. I know that I overshot my target slightly, which led to about 15 min of 0% output. And, that was long enough to snuff out the fire. So, just for the sake of testing, I went with Kingsford today. It was a little unsteady at first. So, I upped P to 4. Now my PID is P=4; I=0.001; D=15. This is working a little better. Don't pay too close attention to the first 20 min or so. That was me bringing the temp up slowly by raising my target bit by bit.


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Very close

Darren C. said:
@Bill - I hope I'm not too late. You can breathe now:).

I'm doing another test today. This time, at 225 with a weber chimney of Kingsford. I tried lump last night twice, but the fire went out both times. I'm not too sure if it's me or the lump. I'll figure that out later. I know that I overshot my target slightly, which led to about 15 min of 0% output. And, that was long enough to snuff out the fire. So, just for the sake of testing, I went with Kingsford today. It was a little unsteady at first. So, I upped P to 4. Now my PID is P=4; I=0.001; D=15. This is working a little better. Don't pay too close attention to the first 20 min or so. That was me bringing the temp up slowly by raising my target bit by bit.


NUKHw2wl.png
Click to expand...

This is very close to being perfect, you P gain might be smudge to high but this is a decent tune of the PI portion of the PI you notice how the ringing is reduced over time, this is the integral taking over from the proportional. Yes a large D on the Akorn is typical, the Akorn will get out of hand if you overshoot (flameouts, if your grill is well sealed). What works the best is to find the settings that look like above, then crank up the D until it refuses to reach temps, because it is shutting off too soon then slowly back it off until it reaches the set point. The D term will counter act the P term. Think of the D like a speed limit, it operates on the temperature delta (the rate the grill temperature is changing) this will predict what the temperature will be in the future. Another thing I like to do is never let the servo damper completely close. This will minimize your flameouts from occurring, as this is the biggest risk of this grill. Remember if a mouse farts in this grill it will cause the temperature to rise quickly. I have also come to the conclusion that this grill is not the best for smoking. I have had mine for 2 years now, and I have had a webber smokey mountain also for half that time. I find the webber is more forgiving with smoke, and produces a much better tasting product. It's hard to regulate the Akorn, and also the smoke, since there is almost no air flow in this grill you have to really have a light hand on the smoke. It is so easy to over smoke ribs on the Akorn. I have never found a method to control the smoke, I have one last idea which is setting up a half circle of lump and mixing in wood where I need the smoke then lighting one end of the half circle. As the lump burns thru the wood I get smoke when I need it. The WSM you just mix in about a cup or 8 oz of wood into the lump, and it works. Additionally the WSM is much more forgiving of shooting over temp as it will cool down quickly, and always needs stoking to reach and maintain temperature.
 
Darren you P is way to high your getting oscillation, and your oscillation is increasing not reducing . Half your P value, and that ringing should be reduced. Also your D might be a little high, I run at about half 5-8.
 
Thanks for the well thought out post. I maintained temps like that for around 30 hours. The Akorn is SUPER efficient. It's really ridiculous how efficient it is. But, this might be it's downfall. After a couple of successful test runs, I decided to use it over the 4th to cook ribs and butt. For the life of me, I couldn't get the temps to stabilize. It was a constant effort. I think it may be time for me to throw in the towel on using the Akorn as a smoker.

While making a few attempts to test or cook, I was coming to the same conclusion you did about the Akorn vs. WSM. The WSM will make the HM work harder which would give the HM more control. It would prevent the long periods of overshoot and subsequent flameouts. I had an 18" WSM. For the most part, I enjoyed it. I found the lack of a lid hinge and the lower rack to be pain points. But, mainly I just wanted something bigger. So, I sold it with the intentions of replacing it with either a 22" WSM or a ceramic cooker. Then, I found this Akorn on Craigslist and decided it would be an inexpensive way to dip my toe into the world of ceramic cooking. I have 3 Weber kettles. So, I'm only looking for a smoker. When it comes to grilling things like chops, burgers, chicken and fish, I'm 100% satisfied with my kettles. Well, I don't know if it's my imagination or not, but the burgers on the Akorn do seem to come out more juicy on the Akorn. But, there are a lot of variables that could factor into that. But, I am really just looking for a smoker.

I've been considering a pellet grill, too. Now I think it's between the 22" WSM and the GMG Daniel Boone.
 
Don't give up on the Akorn, it makes an excellent smoker. You just need to keep in mind that it really holds the heat, so you can't let it overshoot too far or a damper will snuff out the fire. One mistake people seem to make is setting the startup MAX fan speed very low, when the HM see's the temp rise to the setpoint slowly it will react slowly tamping things down, which will cause a lot of overshoot and a long choke period which may extinguish the fire.
Start a very small fire (I suggest lump coal), close the lid quickly, don't let the fire build up too long in open air. Set the top vent very tight, start with just the dimples opened. After a few attempts you should be able to make her land right on the setpoint with little overshoot. If you get overshoot sometimes after the temp has fallen a bit (but is still above the setpoint) you can open the lid and and burp the pit a bit, or just put in your food. This will give the fire a bit of oxygen to keep it alive.
There is a learning curve attached to running a tight insulated grill, its a totally different beast compared to a thin walled kettle or smoker. Give it some time, I'm sure you'll figure it out. When I start a low and slow I use a half of a weber starter cube under a small pile of lump, you dont need too much starter fuel it get the fire where you need for low and slow, and don't need much lump to hold it there for a very long time.
 
Thanks for the tips, Ralph. My startup MAX has been 40% most of the time. What percent do you use? It's interesting that the rate of ascent is counter-intuitive. I seemed to have my best luck starting the Akorn when I was setting the fan in manual mode and getting the temp to target by manually adjusting the % output with the buttons. But, my LCD quit working (see my other thread). And, using the buttons in conjunction with the LCD was the only way I knew how to set a specific output. I started a couple of fires that way and it seemed to work pretty well. Speaking of startup MAX, I noticed over the July 4th cook that my startup MAX was behaving more of like a MAX all of the time. I wonder if mine is not functioning correctly or if I am not understanding what "startup" means in this context. Shouldn't the MIN and MAX take over for the startup MAX after some point?

But, beyond startup, it was disappointing that once I got the temp at target, it just wouldn't stay there. The temps were all over the place, using the same PIDs that I had great success with when testing. They never stabilized. I realize that food might change the dynamics somewhat. So, I tried making a few adjustments during the cook. But, nothing helped.
 
I leave the startup Max at 100%, use 1/2 a weber starter cube under a pile of lump, leave the lid open just long enough to see the smoke from the started cube to go away. A Max of about 30% should be good for the akorn, the MAX setting should take over once the pit has hit the target temp.
 
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